The Inverse Monoid of Partial Inner Automorphisms of a Semigroup

We introduce the inverse monoid of inner partial automorphisms of a semigroup – a tool that associates to every semigroup an inverse semigroup. When the semigroup is a group, this inverse semigroup is isomorphic to the group of inner automorphisms with a zero adjoined. We then describe this structure for completely simple semigroups, the full transformation monoid, and the endomorphism monoid of a finite $G$-set when $G$ is a finite abelian group. The paper ends with some open problems.